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Application of metal elements gallium, indium and thallium in the production of electric light sources

Gallium, indium and thallium are the main elements of the third group in the periodic table. Gallium, indium and thallium are not concentrated in nature, and are all scattered elements with soft texture. Gallium has a very low melting point (only 29.78℃), and it can melt into liquid when placed in the palm of your hand. At room temperature, gallium is solid and can be cut with a knife. It can be pressed into thin foil or drawn into filaments, or forged. The special thing is that when gallium condenses from liquid to solid, its volume will expand by 3%, so gallium is usually packed in elastic plastic bags or rubber bags to prevent the container from bursting when gallium solidifies. If it is packed in a glass bottle, don't fill it up.

Gallium has a low melting point and can be made into fusible alloys with zinc, tin, indium, etc. Although gallium has a low melting point, its boiling point is very high (2403℃), which means that from 29.78℃ to 2403℃, gallium is always in liquid state, while mercury boils at 357℃. Therefore, gallium can be used to make high-temperature thermometers. Mercury can only measure temperatures below 300°C, while gallium can measure temperatures below 1500°C.

Gallium can be tightly attached to glass, so it can be made into a good Reflector. Gallium and indium do not change in dry air at room temperature, but thallium is oxidized when it comes into contact with air, and the surface becomes a gray film. Gallium and indium are both soluble in acid or alkali. Thallium is easily soluble in nitric acid but insoluble in alkali. They can all react with halogens. When heated, the three elements can react violently with oxygen and sulfur.

It is worth noting that the compounds of these three elements are all highly toxic, so be careful when using them.

The characteristic spectra of gallium, indium, and thallium are purple, blue, and green, respectively. Light sources made from their iodides alone can be used for decoration. Metal halide lamps made from their iodides have sparse strong line spectra.

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